Abstract

The high temperature phase in , a hydrogen-bonded antiferroelectric/ferroelastic material, was investigated by ac impedance measurements. A Warburg diffusion was manifested in the low-frequency region in the Cole-Cole plots near the ferroelastictransition temperature , indicating a surface instability. The temperature dependent impedance, analyzed by a simple equivalent circuit model, was discussed in view of hydrogen delocalization on the surface.

This work was supported by the Korea Science and Engineering Foundation (Proton Accelerator User Program Nos. M102KS010001-02K1901-01814 and RO1-2005-000-10798-0) and by the Korea Research Foundation (Grant No. KRF-2004-005-C00060 and Brain Korea 21 Project in 2005). The authors also acknowledge the Innovative Cluster Project funded by the City of Seoul. The measurements at the Korean Basic Science Institute (KBSI) are acknowledged.